(2) Clean only contaminated areas and items. Before cleaning, make sure that the cleaning materials and methods will not cause more contamination. Make sure cloths used are clean, dry, and lint-free. Connectors should be completely dry before mating. Fluids left on connectors can have a deteriorating effect on the connector or the system or both.
h. Servicing or Repairing Waste/Water Systems. EWIS in areas adjacent to waste/water systems are prone to contamination from those systems. Use care to prevent fluids from reaching EWIS components while servicing or repairing waste/water systems, and cover exposed EWIS components while working. Operator practice may call for a weak acid solution to be periodically flushed through lavatory systems to improve reliability and efficiency of operation.
Because of the effect of acid contamination on systems and structure, confirm that the system is free of leaks before using such solutions.
i. Servicing or Repairing Oil Systems. EWIS in areas adjacent to oil systems are prone to contamination from those systems. Oil and debris in combination with damaged wiring can present a fire hazard. To minimize the attraction and adhesion of foreign material, use care to prevent fluids from reaching EWIS components while servicing or repairing oil systems.
j. Servicing or Repairing Hydraulic Systems. EWIS in areas adjacent to hydraulic systems are prone to contamination from those systems. To minimize the attraction and adhesion of foreign material, use care to prevent fluids from reaching EWIS components while servicing or repairing hydraulic systems.
k. Gaining Access (Entering Zones). When entering the airplane or working on it, use care to prevent damage to adjacent EWIS components, including wiring or other EWIS components that may be hidden from view (for example, covered by insulation blankets). Use protective boards or platforms for adequate support and protection. Avoid using wire bundles as handholds, steps, and supports. Do not use wiring to hang or support work lights. If wiring must be displaced or removed for work area access, it should be adequately released from its clamping or other restraining provisions to allow movement without damage, and it should be returned to position after work is completed.
l. Applying Corrosion Prevention Compounds (CPC). When applying CPC in airplane zones containing EWIS, use care to prevent CPC from contacting it. Dust and lint are more likely to collect on wire that has CPC on it. Apply CPCs according to the airplane manufacturer’s maintenance instructions.
/s/ Ali Bahrami Manager, Transport Airplane Directorate Aircraft Certification Service 31
Appendices Appendices Appendix A. The Enhanced Zonal Analysis Procedure (EZAP)
Appendix B. Evaluating Whether a Design Change Impacts Previously Approved EWIS ICA and Developing any Necessary New or Revised EWIS ICA as Required by § 26.11(c) or § 25.1729 Appendix C. Definitions Appendix D. FAA Oversight Offices for the Purposes of Part 26 Appendix E. Applicable Regulations and Relevant Preamble Discussion Appendix F. Background Appendix G. Related Regulations and Documents Appendix H. EZAP Worksheets for Use by Applicants
Appendix A Appendix A
1. The Enhanced Zonal Analysis Procedure (EZAP). The figures and explanations on the following pages describe the EZAP process. Before you begin using this logic, you should be thoroughly familiar with the contents and philosophy of this AC and the results the AC and the EZAP seek to achieve.
A-1
Appendix A Identify aircraft zones, including boundaries Figure 1 Enhanced Zonal Analysis List details of zone, for example:
Procedure Access Installed equipment Lightning/HIRF protection features EWIS installation Possible combustible materials YES Does the zone contain EWIS?
NO likely to be, combustible Are there, or are there Is wiring or other EWIS materials in the zone? NO close (2 in/50 mm) components -NO→ to both primary and backup hydraulic, mechanical, or electrical flight controls?
No further analysis is required for the zone.
An inspection or restoration task applicable to EWIS is not necessary for the zone.
Is there an effective task to significantly reduce the likelihood of -NO- accumulation of combustible Select EWIS inspection materials? level and interval See figure 2 YES
CONTINUE THE Define the task and ANALYSIS assign an interval for INSPECTION TASK(S) performing it.
• STAND-ALONE GVI GVI CONSOLIDATED
• DET Consider consolidation with existing IN ZONAL
• Cleaning (Restoration) inspection tasks in systems and INSPECTION
• Any other tasks powerplant and/or zonal programs * identified as applicable and effective to maintain EWIS safety * Section 26.11(b) requires Assign task to EWIS ICA EWIS ICA and fuel tank Assign task to EWIS ICA maintenance program systems and system ICA developed to Maintenance program zonal section powerplant section comply with SFAR 88 be Recommend inclusion in ATA 20 compatible and any Airplanes with ZIPs redundancies between them minimized.
A-2
From figure 1, step 8 Figure 2 05/04/10 Using rating tables, assess zone attributes to determine appropriate level of inspection Step 8 - (examples provided in appendix B of this AC) EWIS Inspection Level and Interval Selection
PROGRAMS WITH ZONAL PROGRAMS WITHOUT ZONAL
INSPECTION PROGRAM INSPECTION PROGRAM Is zonal GVI alone effective YES • List zone description and zone at same interval effective Is GVI of all EWIS in the YES • boundaries for GVI of all EWIS List zone description and for all EWIS in the zone? boundaries for zonal GVI for all EWIS in the zone? in the zone NO NO Define specific EWIS in the Define specific EWIS in the zone for which stand-alone zone for which GVI at more GVI is justified frequent interval is justified Zonal GVI must be augmented Some EWIS requires GVI at with stand-alone GVI and/or more frequent interval and/or DET inspection DET inspection Define specific EWIS in the Define specific EWIS in the zone for which DET is justified zone for which DET is justified Using rating tables, assess likelihood of damage to EWIS in the Appendix A AC 25-27A zone to determine an appropriate interval for each inspection task identified (example provided in appendix B of this AC)
Appendix A
2. Explanation for Steps in EZAP Logic Diagrams. The following paragraphs provide further explanation of each step in the enhanced zonal analysis procedure (EZAP) logic (figures 1 and 2 of this appendix). If you are developing EWIS ICA because you are required to do so by § 26.11(b), then you must use the “representative airplane” as required by that section.
(See paragraph 2c of this AC.) All applicants should, whenever possible, verify the results of the analysis using an actual aircraft (typical airplane that has not been cleaned) to ensure that they fully understand the zones being analyzed. Using an actual airplane will help in determining density, size, types and levels of contaminants or combustible materials, and environmental and accidental damage issues for each zone.
STEP 1: Identify aircraft zones, including boundaries.
According to Air Transport Association (ATA) iSpec 2200, Information Standards for Aviation Maintenance, zones are identified by the airplane manufacturer “to facilitate maintenance, planning, preparation of job instructions, location of work areas and components, and a common basis for various maintenance tasks.” ATA iSpec 2200 contains guidelines for determining airplane zones and their numbering. The EZAP process uses these manufacturer-identified zones. The zones are not created uniquely for EZAP.
However, if the design approval holder or operator has not already established aircraft zones, we recommend that this be done. Wherever possible, the definition of zones should follow a consistent method such as ATA iSpec 2200 (formerly ATA Spec 100), varied only to accommodate particular design constructional differences.
Define the zones, wherever possible, by actual physical boundaries such as wing spars, major bulkheads, cabin floor, control surface boundaries, skin, and so forth, and include access provisions for each zone.
STEP 2: List details of zone.
Within the zone, identify system installations, significant components, lightning and high intensity radiated field (L/HIRF) protection features, typical power levels in any installed wiring bundles, combustible materials (present or with the potential for accumulation) and any other features that may affect EWIS integrity or accumulation of combustibles.
With respect to power levels, the person performing the EZAP analysis should know whether the wire bundle consists primarily of main generator feeder cables, low voltage instrumentation wiring, or standard bus wiring. This information will be used in determining potential effects of deterioration.
Identify any locations where both primary and back-up flight controls are routed within 2 inches/50 mm of a wiring harness or other EWIS components. This information is required to answer the question in step 7.
STEP 3: Does zone contain EWIS? This question eliminates from the EZAP those zones that do not contain EWIS.
A-4
Appendix A STEP 4: Are there, or are there likely to be, combustible materials in zone? This question requires evaluating whether the zone might contain combustible material that could cause a fire to be sustained in the event of an ignition source arising in adjacent wiring. Examples include the presence of fuel vapors, dust/lint accumulation, and contaminated insulation blankets.
• With respect to commonly used liquids (for example, oils, hydraulic fluids, and corrosion prevention compounds) refer to the product specification to assess potential for combustibility. The product may be readily combustible only in vapor mist form. If so, an assessment is required to determine if conditions might exist in the zone for the product to be in this state. You should consider hydraulic fluid to be combustible in a mist form even if the product specification states that it is not combustible in its liquid state.
• Liquid contamination of wiring by most synthetic oil and hydraulic fluids (for example, skydrol) may not be considered combustible. It is a concern, however, if it occurs in a zone where dust and lint are present, because wet or oily surfaces attract dust and lint.
Assess what sources of combustible products may contaminate the zone following any single failure considered likely from in-service experience. For example, consider unshrouded pipes with connections within the zone to be potential contamination sources. Forced air ventilation in a zone tends to blow dust and lint through the air, causing it to lodge on the surfaces of wiring and other EWIS components. Wet or oily surfaces attract more dust and lint. This needs to be considered when you are assessing the possibility of a buildup of combustibles in the zone.
• Avionics and instruments located in the flight compartment and equipment bays tend to attract dust, dirt, and other contamination. Because of the heat generated by these components and their relatively tightly packed installations, you should consider that these zones have the potential for accumulating combustible material. Forced air ventilation is often used in these areas, causing lint and dust to be blown about the area and often resulting in a buildup of dust and lint on the surfaces of wiring and other EWIS components. Always use the EZAP logic for these zones. For flight compartment and equipment bays, the answer to the question in step 4 should be “yes.”
Although moisture (whether clean water or otherwise) is not combustible, its presence on wiring, or other current carrying EWIS components increases the probability of arcing from small breaches in the insulation. This could cause a localized fire in the wire bundle. The fire could spread if there are combustibles in close proximity. The risk of a sustained fire caused by moisture-induced arcing is mitigated in step 5 by identifying a task to reduce the likelihood of accumulation of combustible material on or adjacent to the wiring and other EWIS components.
STEP 5: Is there an effective task to significantly reduce the likelihood of accumulation of combustible materials? Most operator maintenance programs have not included tasks directed towards removing combustible materials from EWIS components or adjacent areas or preventing their accumulation. Evaluate whether accumulation on or adjacent to the EWIS can be significantly reduced.
Though restoration tasks such as cleaning are the most likely applicable tasks, the possibility of identifying other tasks is not eliminated. For example, a detailed inspection of a hydraulic pipe A-5
Appendix A might be appropriate if high-pressure mist from pinhole corrosion could impinge a wire bundle and the inherent zone ventilation is low. Task effectiveness criteria should include considering the potential for damaging EWIS components.
STEP 6: Define the task and assign an interval for performing it.
This step will define an applicable EWIS ICA task to reduce accumulation of combustible materials and an effective interval for performing that task. The defined task should be included as a dedicated task in the systems and powerplant section of the maintenance program. Within maintenance review board reports (MRBRs), it may be introduced under the standard practices section (ATA chapter 20 of the MRBR) with no failure effect category assigned.
Restoration tasks should not be so aggressive that they damage wiring, but should be performed at a level that significantly reduces the likelihood of combustion.
STEP 7: Is wiring close to both primary and backup hydraulic, mechanical, or electrical flight controls? This question is asked to ensure that step 8 logic is applied where wiring is close (in other words, within 2 inches/50 mm) to both primary and backup hydraulic, mechanical, or electrical flight controls, even in the absence of combustible materials in the zone.
For zones where combustible materials are present (as determined in step 4), proximity is addressed in the inspection level definition portion of step 8, and this question need not be asked.
This step addresses the concern that segregation between primary and back-up flight controls may not have been consistently achieved. Even in the absence of combustible material, a localized wire arcing could prevent continued safe flight and landing if hydraulic pipes, mechanical cables, or wiring for fly-by-wire controls are routed in close proximity (within 2 inches/50 mm) to a wiring harness. In consideration of the redundancy in flight control systems, this question should be answered “yes” if both the primary and back-up system might be affected by wire arcing.
On all aircraft type designs, regardless of TC date, alterations performed by an STC holder or a field-approved repair or alteration may not have taken into account the TC holder’s design criteria. We recommend that STC holders assess whether their design changes route wires within 2 inches or 50 mm of both primary and back-up hydraulic, mechanical, or electrical flight control cables and lines. Similarly, air carriers and air operators should assess any field-approved repairs or alterations or other modifications that have been made to their airplanes to identify any added or altered wiring that may be close to flight control cable and lines.
STEP 8: Select EWIS inspection level and interval (Figure 2).
a. Inspection Level. At this point in the analysis, it is already confirmed that EWIS is installed in a zone where the presence of combustible materials is possible and/or the wiring is in close proximity to primary and backup hydraulic or mechanical flight controls.
Therefore, some level of inspection of the EWIS in the zone is required. This step details how to select the proper level of inspection and interval.
A-6
Appendix A
The inspection level and its interval are determined by using ratings tables, which rate characteristics of the zone and how the EWIS is affected by, or can affect, those attributes.
The type of inspection is determined by using the rating tables of EZAP Worksheet 3A (or 3B for airplane models without a dedicated zonal inspection program (ZIP)), whereas the interval for performing the inspection is determined using the rating tables of EZAP Worksheet 4.
Worksheets 3A and 3B use zone size, zone density, and the potential effect of fire in the zone to determine the type of inspection that is necessary.
• Zone size—Zone size determination is based on comparing all the zones in a given airplane model and assessing them in relation to each other. For the purposes of the EZAP analysis, zone sizes are identified as small, medium, or large. For example, the aft cargo bay on a large transport category airplane would be considered a large zone, but the radome on the same airplane would be considered a small zone. The smaller the zone and the less congested it is, the more likely it is that wiring degradation will be identified by a general visual inspection (GVI).
• Zone density—The density of installed equipment, including wiring and other EWIS components, within the zone is assessed in relation to the size of the zone. For the purposes of the EZAP analysis, zone density is identified as low, medium, or high.
Typical factors to consider are the number of components, their relative closeness to one another, and the complexity of these components (for example, multiple electrical, mechanical, or hydraulic connections). For example, the electrical and electronics compartment located in the forward nose section, below the flight deck of most large transport category airplanes, could be considered a high density zone. This is because the relatively small physical area is crowded with avionics equipment and a large number of wires and other EWIS components. An example of a low density zone on some airplanes is the cargo compartment (as defined by the cargo compartment walls and forward and rear bulkheads). Although this is a large zone relative to other zones on the airplane, it has relatively few systems or EWIS components installed in it.
• Potential effects of fire on adjacent EWIS or systems—This question should be answered from the point of view that a fire has occurred. So the question to be answered is what is the effect on the safe operation of the airplane should a fire occur.
This assessment should include consideration of the potential for loss of multiple functions and the resulting effect on continued safe operation of the airplane. The presence of flammable fluids should also be considered, although design features such as shrouds over the fuel line can be considered to mitigate the likelihood that the fuel will be a source of fuel for a fire. Base the determination of potential effects of a fire on adjacent wiring and systems on knowledge of what airplane systems are in the area under analysis (in other words, what is in the zone) and how loss or degradation of these systems could affect safe operation. The rating system developed should take these potential effects into account.
If a zone does not have mitigating design features that would reduce the adverse effects of a fire, then the potential effects of a fire should be rated higher (for example, A-7
Appendix A medium or high). Credit for fire mitigation capability can be given to zones that contain a fire detection and suppression system, or a zone that is designated a “fire zone.” Potential effects of a fire in such zones could then possibly be rated at a lower level. Consideration can also be given to whether the fire could be easily detected by crewmembers or passengers and to whether, if there was a fire, it could be extinguished or controlled by available means. Fire can result in severe outcomes, such as wire-to-structure or wire-to-wire shorting and arcing, in areas such as the cockpit, electrical power centers, and those that contain power feeder cables, which are subject to chafing, if they have flammable materials close by. A fire in these areas could present a high risk to continued safe flight and landing.
Potential effects of fire must also be considered when wiring is in close proximity (within 2 inches/50 mm) to both primary and backup flight controls. A GVI alone may not be adequate if a fire caused by failure of the wiring poses a risk to aircraft controllability.
At minimum, all EWIS in the zone will require a GVI at a common interval. For operators with a ZIP, this may be defined as a zonal GVI. For operators without a ZIP, it is a GVI of all EWIS in the zone.
The logic in figure 2 begins by asking a question:
• For airplane models with a ZIP, the logic asks: “Is zonal GVI alone effective for all EWIS in the zone?”
• For airplane models without a ZIP, the logic asks: “Is a GVI of all EWIS in the zone at the same interval effective for all EWIS in the zone?”
This step calls for consideration of whether there are specific items or areas in the zone that are more vulnerable to damage or contamination than others and thus may warrant a closer or more frequent inspection.
Such a determination could result in selection of a more frequent GVI, a stand-alone GVI (for operators with a zonal inspection program), or even a detailed inspection (DET). The intent is to select a DET of EWIS only when it is determined that a GVI will not be adequate. The person performing the EZAP should avoid unnecessarily selecting DET where a stand-alone GVI is adequate. Over-use of DET dilutes the effectiveness of the inspection.
The level of inspection required may be influenced by tasks identified in step 5 and step 6.
For example, if you have selected a cleaning task in step 5 and step 6 that will minimize accumulation of combustible materials in the zone, this may justify selecting a stand-alone GVI instead of a DET for the wiring in the zone.
b. Selecting an Inspection Interval. The inspection interval is determined by using a rating system that rates the likelihood of accidental damage and the hostility of environmental factors.
A-8
Appendix A The rating tables are designed to define increasing inspection frequency based on increasing risk of accidental damage and increasing severity of the local environment within the zone.
Refer to EZAP Worksheet 4 in this appendix.
The example “Interval Determination” table on EZAP Worksheet 4 provides a range of intervals you can choose from. Please note that these intervals are only an example. The particular intervals chosen should be compatible with the interval framework used in the existing maintenance or inspection program as detailed in the current MRBR. Your choice of interval should be based on the reasons for assigning specific rating values for hostility of environment and likelihood of accidental damage. You should also use your knowledge of the types of EWIS components to be inspected.
As an example, for a hostility of environment rating of 3 and a likelihood of accidental damage rating of 3, the table gives a range of inspection intervals. It says that the inspection should occur as frequently as every A check but the interval could be as long as once every 1C check. You should base your choice on the reasons that a 3 rating was assigned.
• The importance of assessing likelihood of accidental damage is that the higher the likelihood of accidental damage from multiple sources, the more frequent the inspection task should be. If, on the other hand, all of the factors except one have been rated as a 1, then the inspection interval could be somewhat longer.
• The choice of the inspection interval should also be based on what type of environment the EWIS is located in. Just as with the ratings for likelihood of accidental damage, the more the EWIS is exposed to various harsh environmental conditions, the more frequent the inspection interval should be. You should consider the assigned ratings from both of these tables—“Hostility of Environment” and “Likelihood of Accidental Damage”—and use sound maintenance judgment to assign the inspection task interval.
The selection of inspection tasks possible in this step is specific to whether the maintenance program includes a zonal inspection program (ZIP) or not.
For ZIP programs, the possible inspection tasks are:
• Zonal GVI
• Stand-alone GVI
• DET For non-ZIP programs, the possible inspection tasks are:
• GVI
• DET At the conclusion of this step you will have determined the required inspection level and interval for wiring in the zone. Task consolidation in step 9 allows consideration of whether A-9
Appendix A an inspection selected as a result of this analysis can be considered accomplished as part of the existing maintenance program.
STEP 9: Consider consolidation with existing inspection tasks in systems and powerplant and/or zonal programs.
This step in the procedure examines the potential for consolidation between the tasks derived from the EZAP and inspections that already exist in the maintenance program. Consolidation would require that the inspections in the existing maintenance program are performed in accordance with the inspection definitions provided in this AC. Consolidation with the fuel tank ICA is required by § 26.11(b) where possible. Compare new tasks identified by the EZAP logic against existing tasks in the maintenance program to ensure that:
a. Tasks are compatible with each other. Existing maintenance tasks and EZAP-generated inspection or maintenance tasks (such as restoration tasks) should not compromise or negate each other. For example, an EZAP-generated task should not compromise existing fuel tank system wire maintenance requirements (for example, those generated by SFAR 88) such as separation or configuration specifications.
b. Task intervals are aligned to the maximum extent possible so undue disturbance of EWIS and other systems located within the zone does not occur. However, the inspection interval you choose must ensure that the intent and reason for the EWIS inspection is not compromised. The EZAP-generated task interval is determined by completing EZAP Worksheet 4 in this appendix.
Example:
Results of the EZAP for a particular zone indicate that using an existing zonal GVI is an effective inspection task for all of the EWIS in the zone. The analysis should be continued to determine the appropriate inspection interval (EZAP Worksheet 4). If the results of the analysis contained on EZAP Worksheet 4 indicate that the EWIS inspection interval is greater than the interval for the existing zonal GVI, the existing zonal GVI interval should be used for the EZAP-identified inspection task. The existing zonal GVI interval cannot be escalated solely based on results of the EZAP analysis. The EZAP only analyzes the need for inspection type and frequency for EWIS within a zone. It does not analyze all of the systems in the zone. Therefore, its results cannot be used as the sole reason to escalate an existing zonal inspection task.
c. Redundant (or duplicate) tasks are consolidated into a single task.
For inspection programs that include a zonal inspection program (ZIP):
• You should not adjust the interval of the stand-alone inspection to match the interval of the existing zonal inspection solely for the purposes of aligning the separate task intervals. Task intervals should only be aligned if the interval will ensure that the safety objectives of identifying the stand-alone GVI in the first place can be met. One A-10